Translating circuits



July 3, 1928. 1,675,876 H. 8. BLACK TRANSLATING CIRCUITS Filed Feb. 3, 1925 Patented July 3, 1928.

UNITED STATES PATENT OFFICE.

HAROLD S. BLACK, OF NEWARK, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGNMENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION OF NEW YORK.

'TRANSLATING CIRCUITS.

Application filed February 3, 1925. Serial No. 6,528.

This invention relates to translating cipcuits, and is particularly adapted for use In carrier wave signaling systems.

An object of the invention is the provision of a simplified circuit for the control of one wave by another, for signaling or other purposes.

-A related object of the invention is to provide a novel form of balanced modulator in which the unmodulated wave components are effectively balanced out, and the sideband alone transmitted.

Another object of the invention is to provide a translating circuit which may be connected in a carrier wave signaling system'to act either as-a modulator or asa detector according to Whether the energy is being transmitted or received.

It is common practice in carrler wave signaling systems to employ balanced modulatorsand detectors which include a pair of electron discharge tubes so connected as to emphasize the production of certain wave components and to neutrallze the production of other components.

Patent No. 1,449.382 to J. R. Carson, dated March 27, 1923, for example, discloses a type of balanced modulator for suppressing the transmission of each of the input waves and for producing in the output of the modulator only Waves which. represent the combination frequencies and the double frequencies of the impressed waves.

The principle of operation of balanced modulators of this general type is now Well known, and need not berepeated except so far as it is considered necessary in pointing out the distinguishing features of the present I invention. The system of the Carson patent, however, depends upon plate current modulation, while that of the present invention depends upon grid current modulation.

stants depending upon the tube characteristics.

If another discharge tube having substantially the same constants, a, b, 0,. etc, be chosen. the output I from this discharge device, due to a similar impressed wave, will be substantially I =ao +bv +co, It is found in practice that all terms in this series after the second power term be, may

be neglected for most purposes. It is also obvious that the first term, which simply represents the repeating property of the device without any frequency modification, plays no part in the modulation process. The property represented by" the second term or}, however, is commonly made use of for effecting the modulation of one input wave by anotherand fordemodulating or detecting by combining input wave components.

Since one object of using a balanced modulator is to suppress the transmission of the unmodified frequencies which represent the impressed waves uncombined with each other and otherwise unchanged, the two dischargedevi'ces are to be so connected relative to the impressed waves as to cause the wave of unmodified frequency that is transmitted by one of the discharge devices to be neutralized by that transmitted by the other. If the input wave o impressed on one-electron discharge device is reversed in sign relative to that impressed on the other, that is, if the two waves have a phase difference of 180, and the output currents are then added, the desired result is accomplished as is indicated in,the following equation, in

which the relatively unimportant higher power terms 'are neglected:

I =cw,+bo, I ao,+ 611, T,+I 2b11, Such a balanced modulator comprises a pair of three-electrode electron discharge tubes connected in opposition or push-ball relation. The input or control electrodes are so connected to an incoming line that one control electrode is made positive when the other is made negative, and the output circuits of the tubes are so connected through a repeating coil to an outgoing line that an increase of current in one output circuit has an effect upon the outgoing line similar to that of the simultaneous decrease of current in the other output circuit.

In a circuit of this type the windings of the output repeating coil in the two branches.

' output circuits of the tubes oppose and substantially neutralize each other with respect to the secondary winding. In this way the unmodified frequencies which represent the impressed waves uncombined are substantially balanced out in the modulator and only the side band produced by modulation is transmitted. The completeness of this action is dependent, however, upon the tubes being identical as to the properties represented by the constants a and b in the above equation, and it is also dependent upon the current I being completely added to the current 1,. Since this addition of the two output currents represents in part really the cancellation of the undesired component represented by the first power term cw even if the current I from the first tube is exactly equal to I but if the addin involve both I, of the component (to, appearing in the output of the tube combination.

Substantiallythe same result is obtained in balanced modulators and detectors which function does not completely depend, upon grid current modulation. That is, by balancing the output of one tube against that of the other, even though modulation takesplace in the grid circuits, and by properly associating, the output circuits with an outgoing line the current components which are differentially impressed upon'the grid circuits may be suppressed from transmission.

The present-invention provides a simplified translating circuit in which the unmodified frequencies which represent the impressed waves uncombined with each other are substantially suppressed from transmission.

In the preferred form" of the invention, modulation is produced in the input circuit 'of a balanced modulator by the action of an impedance included in the input circuit thereof. A high impedance choke coil having two windings is included in the output circuit of the balanced modulator in such a way that the windings act in series aiding as to the wave components which are differentially impressed upon the individual tube input branches, and hence offer a high impedance to the passing of these waves. These windings, however, are connected in and I there will be a residue parallel opposing relation as to the sideband produced by modulation, and hence this component alone appears in the common branch of the plate circuits. An outgoing transmissionline is coupled to the common plate circuit branch of the modulator and hence the sideband alone is transmitted to the line.

The invention possesses certain important advantages over systems of the prior art. By producing modulation in the modulator input circuit it is possible to employ a high impedance choke coil in the output circuits, which could not be employed in the case of a plate circuit modulator, but which improves the quality of grid circuit modulation. The windings of the choke coil in the output. circuits moreover, cooperate to suppress the currentcomponents which are transmitted in series t-herethrough from the plate of one tube to the plate of the other. This circuit arrangement serves effectively to compensate for unavoidable differences in the characteristics of the modulator tubes and in the corresponding branches of the divided circuits associated therewith.

The invention also provides a highly efiicient bilateral translating circuit for use at either terminal of a single channel carrier wave signaling system. Such a system may be of the carrier transmission type'in which the carrier is transmitted along with the sideband, or may be of the carrier suppression type in which the unmodulated carrier is balanced out and the sideband alone transmitted. In either case, in accordance with the invention, the modulating element operates both as a modulator and as a detector in the same circuit so that only one such element is needed at each terminal for two-way operation.

\Vhen used in this connection the invention not only provides an economical and efiicient translating circuit adapted to function either as a modulator or as a detector according to whether the energy is being transmitted or received, but alsomaterially decreases the cost of the terminal, filters which are employed in systems of this type. In such a system, if the carrier and voice frequency components are not suppressed in the balanced modulator or detector, as the case may be, it is necessary that the terminal filters be so designed as to prevent these frequencies from being transmitted-to the line or to the subscribers station, all of which adds to the expense of ,the filters. By means of this invention, however, the terminal filters are not required to discriminate against these frequencies since they are completely suppressed in the terminal translating c1rcu1t.

lVhile the invention is described particularly with reference to its application to line-wire carrier wave systems, it is to be understood that it' is equally applicable to any signaling system wherein signals are transmitted by means of a high frequency carrier wave modulated in accordance with signals.

The various features and advantages of the invention will appear from the consideration of the following description taken in connection with the accompanying drawing, in which:

Fig. 1 is a circuit diagram of a modulator 'ual paths 4 and 5 are connected between the filaments and grids of the two tubes.

An incoming line 6 is associated with the modulator input. circuits through a transformer 7 The other terminal of the line 6 may be associated with a source of signaling variations, not shown. A source of sustained high frequency waves 8 is also connected to the input circuits of the modulator across the incoming line 6 by means of a coupling coil 9.

The circuit illustrated is of the typein which modulation is produced in the input circuits of the modulator by the action of an impedance included therein. Such an impedance may be represented by high resistan'ce elements 10 and 11 included in the input paths 4: and 5, respectively. This method of producing grid current modulation is disclosed in British Patent 247,626, and need not be. here described in detail.

Parallel modulator output circuits comprising a common path 12 and individual paths 13 and 1 1 are connected between the filaments and plates of the tubes 1 and 2. A battery 15 and choke coil 16 are connected across the common path 12 to supply a constant space current to the two tubes. An outgoing line 17 is associated with the mod ulator by means of a transformer 18, the primary of which is included in the common output path 12. The condenser 19 may be included in the path 12 to prevent the flow of direct current through the primary winding of transformer 18.

It will be seen from the above that carrier waves from the source 8 are differentially impressed upon the respective control elements of the tubes 1 and 2, and that at the same time voice or other modulating waves from the line 6 are similarly impressed upon the said control elements. According to the well known action of grid current modulators, these waves are combined in the tube input circuits, and the combination frequencies, together with the unmodified components, are impressed upon the tube output circuits.

According to'a feature of the invention, the unmodified wave components are balanced out in the output circuits of the modulater, and only the sideband produced by modulation is transmitted. To accomplish this, high impedance choke coil windings are included in the plate circuits of the modulator to prevent the unmodula'ted wave components from passing into the common path 12 01 theoutput circuits, and the sideband product of modulation alone appears in the common path 12 to which the outgoing line 17 is coupled..

A highly inductive choke coil 20v is included in the output circuits of the balanced modulator between the common path 12 and the individual path 13, and between the common path 12 and the individual path 14, respectively." The windings of this coil are connected in the circuit in such a way that they act in series aiding as to thewave components which are differentially impressed upon the tube input circuits, and hence ofier a high in'ipedance to the passage of these waves. The windings of coil 20, however, are connected in parallel opposing relation as to the sideband produced by modulation, since the sideband components flow between the plate and the filament inthe same direction in each branch of the divided circuit, and this component alone appears in the common path 12 of the plate circuits. Since the outgoing line 17- is coupled to the common path 12 in which only the sideband components are flowing, it is evident that the sideband alone is transmitted to the line.

Fig. 2 illustrates a terminal of a single channel carrier wave signaling system in which a bilateral translating circuit is adapted for use both as a modulator and as a detector so that only one such elementis needed for two-way operation.

In this system, two conversations may be carried on simultaneously over a single transmission line ML, one by means of ordinary speech frequency currentsand the other by means of carrier currents modulated in accordance with signal variations.

At the terminal station a low frequency line L,, which may be an ordinary telephone or telegraph line, and a carrier channel C are coupled to the line ML by means of a high frequency composite set comprising a low pass filter LP and a high pass filter HP. A second low frequency line L for supplying signal variations to be transmitted as modulations of a carrier wave is connected to the channel O through a low pass filter LP,.

. The bilateral translating circuit including the modulator-detector and the source of carrier waves 8 is connected to the channel 0 at a point between the low pass filter LP and the high pass filter HP by means of a hybrid'coil H. The carrier source 8 is connected to one pair of terminals of the line windings 21 of the hybrid coil, the opposite terminals of which are connected to the channel C. The input circuit of the modulator-detector is connected across the bridge points of the line windings 21. The series winding 22,- which is coupled to the line windings 21-of the hybrid coil, is connected to the outgoing circuit 17 in series with the common path. 12 in the output circuits of the modulator-detector. A resistance 23 is connected across the terminals of the-primary winding of the transformer 7 in the input circuit of the modulator-detector to provide a uniform input impedance. A condenser 19, similar to that shown in Fig. 1 is included in series with each of the conductors of the circuit 17.

Low frequency currents originating in the low frequency line L pass through the low pass filter LP and the hybrid coil H into the balanced modulator-detector. These low frequency currents, however, are prevented from passing to the transmission line ML by the high pass filter HP which does not pass currents comprised within the voice range. There is likewise fed into the modulatordetector the carrier current from the source 8. The unmodulated components are sup ,rcssed in the output circuits of the moduator-detector in the manner described above, and the sideband components appearing in the common path 12 of the output circuits are transmitted through the conductor 17 and hybrid coil H to the channel C. The

sideband component which is thus impressed.

upon the channel C is transmitted, through the high pass filter HP to the line ML.

Since the filter HP is not required. to discriminate against the unmodulated carrier componentwhich is entirely balanced out in the ouput circuit of the modulator-detector a much cheaper filter will serve in this position than has heretofore been possible. It is well known, of course, that if the hybrid coil H is accurately balanced the carrier current from the source 8 which is impressed upon one pair of terminals of the line winding 21 will not be transmitted to the opposite 'pair of terminals of the line windings which are connected to the channel C.

Furthermore, the filter HP is not required to discriminate against amplified voice currents from the output of the modulator-detector since these currents are effectively balanced out in the manner described above. If this balance is not substantially perfect, then even if filter HP is designed to substan tially suppress volce currents from line L lator or detector, of course, is not required to be incorporated in the terminal filter. Such filters may, therefore, be constructed more cheaply than heretofore.

In receiving signals from the distant terminal, not shown, the bilateral translating circuit serves as a detector. The incoming sideband is transmitted through the high pass filter HP to the channel C, but is prevented. from being transmitted to the low frequency lines L or L by the low pass filters LP and LP,, respectively, which do not transmit frequencies above the essential voice range. The incoming sideband frequency appearing in the channel C passes through the hybrid coil H into the modulator-detector in the input circuit of which it is combined with the carrier waves from the source 8. 4

In this case, since the sideband and carrier waves are diiferentially impressed upon the input circuits of the modulator-detector, thesefrequencies will be balanced out in the output circuits thereof. The voice currents produced by demodulation, however, appear in the common path 12, whence they are transmitted through the circuit 17, hybrid coil H and low pass filter LP to the low frequency line L V The invention set forth herein is, of course, susceptible of 'various modifications and adaptations not specifically referred to, but included within the scope of the appended claims.

What is claimed is 1. An electric system comprising divided input and output circuits, means for supplying different wave's to said input circuits, means in said input circuits for combining said waves to produce combination frequency components of the supplied waves, and means in said output circuits offering a high impedance to the unmodified wave. components flowing therein,- said means offering low impedance to the combination frequency components flowing in said output circuits.

2. In a wave combining circuit, a pair of similar wave distorting devices, input 'and output circuits therefor, a plurality of sources of waves to be combined connected differentially to the input circuits of said devices, an outgoing circuit, said output cirnationfrequencies of said impressed waves,

outgoing circuit, and means oflering high impedance to the flow of unmodified wave components in said output Circuits and low impedance to the combination frequency components. V p I 3. An electric. system comprising divided input and ,output'circuits, means for supplying Waves having dlfililliChaIflCteIlStlCS to said input circuits, means in the input circuits for modulating one of said waves in accordance with the other, andhighly inductive impedances connected in said output circuits in series aiding as to the unmodified Wave components and in parallel opposing relation as to the sideband p-rodficed by modulation, r

a. An electric system comprising divided input and output circuits each having a common branch, means for supplying Waves having difie'rent characteristics to said input circuits, means in the input circuits for combining said waves to produce combination frequency components of the supplied Waves, highly inductive impedances connected in said output circuits in series aiding as to the unmodified 'wave components and in parallel opposing relation as to the combination Waves flowing therein, whereby only the combination waves appear in the common branch of the outputcircuits, and an outgoing line coupled tosaid common out-put branch to transmit said combination Waves.

5.Ina Wave combining circuit, a pair of electron discharge devices, having cathodes, anodesand control elements or grids, grid and anode circuits therefor, means for applying diiferenti'ally to the grid circuits each of a plurality of Waves to be combined, means in the grid circuits producing distorted grid current in response to the waves so applied, means in the anode circuits offering high impedance to components of the frequencies of the Waves so applied and low impedance to the sum and difference frequency components of the waves so applied, and means connecting said output circuits cumulatively to a Work circuit. f 1

6 In a Wave combining circuit, cathode and anode'means providing a pair of discharge spaces, control. elements for control ling the impedances of said discharge spaces, a control circuit and an anode circuit for each discharge space, means to impress differentially on said control circuits each of a plurality of waves of difi'erent frequency, means producing current, variations in the control circuits in response to the Waves so impressed and out of direct proportion to the voltages of said waves, means in the anode circuits oifering greater impedance to the flow of discharge currents in said spaces of the frequencies of said impressed Waves than to components representing the combiand means coupling said anode circuits cumulatively to a work circuit.

7 In a wave combining circuit, a pair of similar space discharge devices, each having a cathode, an anode and a grid or control element, grid circuits and anode circuits therefor, a plurality of wave sources, connections applying each source diiferentially to said grid circuits, saidvsources being of sufficient yoltage to produce current in each grid circuit, a dissipating impedance in each grid circuit Wherebydistorted grid currents are produced in response to said Wave sources, an inductance coil in each anode circuit, said coils being mutually aiding for anode currents flowing in the anode circuits in series, and mutually opposing for currents flowing in the anode circuits in parallel, an outgoing circuit, and means coupling said anode circuits in parallel-aiding relation to I said outgoing circuit.

8. An electric system comprising divided input and output circuits each having a common branch, means for differentially impressing waves having diiferent characteristics upon said input circuits, means in' said input circuits for combining said Waves,

highly inductive impedance elements connected in said outputcircuits in series aiding as to the unmodified wave components and in parallel opposing relation as to the combination waves flowing therein, whereby only the said combination Waves appear in the common branch of the output circuits, and an outgoing line coupled to said common output branch to transmit said combination Waves.

9. A. wave translating system comprising input and output circuits, means for supplying waves of different frequencies to said input circuits, means included in said input 1 5 circuits for combining said waves to produce combination frequency components of the supplied Waves, and means in said output circuits ofiering high impedance to the unmodified Wave components flowing therein, of the frequency of each of the supplied waves and to theiflow of speech currents therein and low impedance to the flow of the modulation components thereinderived from said grid circuit, and an outgoing circuit coupled to said anode circuit. v

11. In a wave translating system, sources of waves of diiferent frequency, a space discharge device having an input and an output or anode circuit, said sources of waves being coupled to the input circuit means in the input circuit producing current components therein representing modulation components of the waves from said sources, a retard coil modulated components similar but opposed to those produced in said anode circuit, said retard coil having a winding in said second circuit, said windings being mutually aiding as to their impedance effects in said anode circuit for unmodulated components and mutually opposing as to their impedance effects in said anode circuit for the modulated components. a

12. A wave translating system comprising a pair of electron discharge devices, divided input and'output circuits therefor, means for impressing waves-having different character istics thereon diiferentially with respect to said input circuits, means included in said input circuit for combining said waves, means in said output circuits to ofler a high impedance to the waves which are impress-ed diiferentially upon said input circuits and to ofler a low impedance to the combination waves, and means to transmit said combination waves.

13. A wave translating system comprising divided input and output circuits each having a common branch, a pair ofelectron discharge devices connected in push-pull rela- 1 tion between said input and output circuits, means for impressing waves having difierent characteristics upon said system differentially with respect to said input circuits, means includedin said input circuits for modulating one of said waves in accordance with another, wave, highly inductive impedance elements connected in said output circuits in series aiding as to the unmodified wave components andin parallel opposing relation as to the side band produced by: modulation,

whereby only the sideband component ap-- pears in the common branch of said output circuits, and an outgoing line coupled to said common output branch to transmit said sideband component. a r

14. A duplex signaling system comprising a transmission line, a hybrid coil having two line winding terminals connected to said transmission line, a source of carrier waves connected to the opposite terminals of said line windings, a bidirectionally conducting modulator-detector having an input circuit connected to the bridge points of said line windings, and an output circuit connected to the series Winding of said hybrid coil.

15. A duplex signaling system comprising a transmission line for supplying waves having "different characteristics, a bidirectionally conducting modulator-detector associated with said line and comprising a pair of electron discharge devices and divided input and output circuits therefor, means included in said input circuits for combining the waves flowing therein,'and highly inductive impedances connected in said output circuits in series aiding as to theuninodified wave components flowing therein and 'in' parallel opposing relation "as to the modified -waves therein. 1 r

16. A duplex signaling system comprising a transmission line for supplyingwaves having different characteristics, a hybrid-coil having two line winding terminalslconnected to said transmission line, a source "of carrier waves connected to the opposite terminals of said line windings, a bidirectionallyic'on Y ing the waves flowing therein, and highly inductive impedance elements connected in said output circuits in series aiding as to the unmodified wave components and in parallel opposing relation as to the combination waves flowing therein, whereby only the said combination waves appear in the common branch of said output circuits and are trans mitted to said line.

17. A system according to claim 1 in whic the recited impedance-offering means in the output circuits comprises means for. adding inductive reactance to the output circuits for the specified frequency components.

In Witness whereof, I hereunto subscribe my name this 28th dayof-January A. D., 1925.

HAROLD s. BLACK. 

